United stall without the spark of Beckham

Manchester United are going through a crisis by their standards and I don't think it's all down to problems with their back four. I've felt for a while they have never really replaced David Beckham and that was obvious again against Porto.

Ruud van Nistelrooy admitted this week that United miss the England captain and people might assume he was talking about Beckham's ability to deliver quality crosses, free-kicks and passes. But it's about more than that.

Beckham gave United something defensively as well as going forward. He did a lot in terms of filling in holes and getting back to help the backline. At the moment United are a bit easy to get at down the sides, particularly on their right.

Because people talked about Beckham's crossing and set pieces, his defensive work was often overlooked. He had a good little tandem going with Gary Neville, which was probably strengthened by the fact that they're friends. If one of them was in trouble the other would bust a gut to help out.

I don't see the same barrier being put up down that flank now, whoever the personnel are. Opponents are able to get more crosses into the box and that's the last thing United need at a time when their backline is weak, particularly in the air, without Rio Ferdinand.

The problem is nobody's come to the fore who knows that right-hand position inside out and can fill in holes and break out. For major matches, Cristiano Ronaldo is basically a substitute, someone who can come on and often stretch teams. He can get at people in the last third but when the ball changes hands he's not the best at the moment at offering protection.

In fairness to him, I think he'd have been signed even if Beckham hadn't gone because he'd been earmarked by Sir Alex Ferguson as one for the future. But I think Alex hoped Kleberson would play on the right a lot this season and that hasn't happened.

Kleberson's a World Cup winner and you'd imagine he would be trusted for a game like Porto but he was on the bench. He's probably better suited to playing on the right than Paul Scholes, who got the nod there, so I guess he's not developed as United had hoped.

Scholes looked wasted in that wide role. All I can think is Alex wanted maximum energy in midfield and players who knew how to defend and get round the ball. He's tried all sorts of people on the right. It says something that Scholes, Ronaldo, Kleberson, Ryan Giggs and Ole Gunnar Solskjaer have all been used there, as have David Bellion and Chris Eagles.

United could do with being strong across midfield because the defence is struggling. It's makeshift because of Ferdinand's suspension and people are being moved around. At times on Wednesday it was a bit like watching United in Madrid last season. A lot of players stood there mesmerised. They didn't have the stature you'd expect from United players.

The belief also seems low, which is unusual, and it's not a foregone conclusion that United will overturn a 2-1 deficit, particularly without Roy Keane. The thing in their favour is that Porto have a dreadful record in England.

I think United need one of those high-tempo performances which will put Porto straight on the back foot. If they let Porto bed in, it could be difficult because you can see that Porto have some very good ball manipulators and are capable of scoring.

Things should be more straightforward for Arsenal and Chelsea in their second legs. They'll have to do something badly wrong to blow one-goal leads at home.

Arsenal didn't defend at the level they're capable of at Celta Vigo but I wouldn't be over-concerned by that. I always felt they could step up a gear if they needed and only complacency can cost them a quarter-final.

They'll know they won't be able to afford anything less than absolutely top level against the likes of Milan or Madrid and they should have learned two lessons in Vigo. It ought to have given them a reawakening about the way they deal with set plays and reminded their wide midfielders to work harder defensively. They can't afford to leave flank defenders exposed the way Gaël Clichy was in the second half.

The big test for Chelsea is whether they can deal with the expectancy against Stuttgart. I'm not totally sure they have that in their locker yet, but they should come through if they play close to their best because I don't over-fancy Stuttgart after seeing them at Old Trafford.

I hope Chelsea try to put Stuttgart under the cosh straight away and try to land the knockout. Of course they have to be sensible but just trying to see the game though with their 1-0 advantage would be dangerous.